It doesn't build without it, it then tries to use a generated spawn
header and fails with something like:
```
CC gl_linkedhash_list.o
In file included from /home/builder/.termux-build/m4/src/lib/execute.c:72:
./spawn.h:690:17: error: use of undeclared identifier 'POSIX_SPAWN_RESETIDS'
[(((POSIX_SPAWN_RESETIDS | POSIX_SPAWN_SETPGROUP
^
./spawn.h:690:40 CC gl_list.o
: error: use of undeclared identifier 'POSIX_SPAWN_SETPGROUP'
[(((POSIX_SPAWN_RESETIDS | POSIX_SPAWN_SETPGROUP
^
./spawn.h:691:19: error: use of undeclared identifier 'POSIX_SPAWN_SETSIGDEF'
| POSIX_SPAWN_SETSIGDEF | POSIX_SPAWN_SETSIGMASK
^
```
Solve this error by depending on libandroid-spawn instead.
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